1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and, more particularly, to a CMOS (Complementary Metal Oxide Semiconductor) operational amplifier.
2. Description of the Background Art
In general, in order to make each pixel be radiated to desired colors, display devices displaying images through an LCD (Liquid Crystal Display) use a driving IC (Integrated Circuit) driving each pixel of the LCD to a gray level of red (R), green (G) and blue (B) corresponding to the desired colors.
Especially, unlike a PDP (Plasma Display Panel) in which a gray level is selected by the width of high or low intervals of a pulse like a pulse width modulation method, in the driving IC driving the LCD of a voltage driving method in which a gray level is selected by a voltage level, each pixel of the LCD connected to each output channel is operated as a gray level of R, G and B which correspond to a desired color.
Among display devices using the LCD, an LCD monitor or an LCD television receiver does not require a high speed driving IC because as many pixels as needed for the resolution are constructed in a matrix form and one driving channel is connected to each pixel. Thus, it is not difficult to design or fabricate the driving IC of the display devices.
However, in case of an LCD projection display device which forms a large screen in a projection method, since the driving channels that can be connected to the high resolution LCD are limited, the driving channels should be multiplexed at a high speed so as to be driven.
Thus, the driving IC used for the projection display device requires a faster driving speed for multiplexing the driving channels than the driving speed of the driving ICs used for the LCD monitor or the LCD television receiver. Herein, an output voltage of the driving IC used for the LCD projection display device is generally in the range of about 10V˜15V.
In order to satisfy all the conditions, it is advantageous that the driving IC is implemented as a bipolar junction transistor (BJT), which has a quick fabrication process. Thus, generally, the driving IC is implemented as the BJT which can be driven at a high speed while satisfying the range of the high output voltage.
However, such a driving IC has the following problems. That is, the conventional BJT operational amplifier with the driving IC incurs a high fabrication cost and it is difficult to integrate the BJT operational amplifier together with other IC implemented as the currently commercialized CMOS.
In addition, a generally used conventional 2-stage CMOS operational amplifier, which has been implemented as the CMOS to solve the problems, also has problems that it can hardly charge or discharge a large-capacity capacitive load at a high speed and an input offset voltage among driving channels can be increased.